Rectifier.



UNITED STATES PATENT OFFICE.

GEORGE STANLEY HEIKLE, OI SCHENECTA DY, NEW YORK, ASSIGNORTO GENERAL ELECTRIC COMPANY, A.

v RECTIFIER.

coaromrron on NEW YORK.

Specification of Letters Patent. Patented May 14, 1918.

1914, Serial No. 865,836. Divided and this application Med January 15,

1916. Serial No. 72,828.

To all whom it may concern:-

Be it known that I, GEORGE STANLEY MEIKLE, a citizen of the United States, residing at Schenectad county of Schenectady, State of New York, have invented certain new and useful Improvements in Rectifiers, (division of my application filed October 9 1914, Serial No. 865,836,) of which the following is a specification.

The present invention relates to the rectification of alternating current of a current and of the mercury arc rectifier, and is embodied in a device having an electron-emitting cathode, andan anode or anodes.

My device is distinguished in one aspect from various prior devices containing an incandescent cathode by the presence of an inert gas at a considerable pressure, as distinguished, for example, from the highly attenuated residual trace of gas present in an envelop exhausted to what is termed a lamp vacuum. Although no very definite lower limit of pressure can' be assigned, for practical purposes the gaseous pressure should not be much below one millimeter of mercury as at ve rapid electrical dlsintegration of the oathode occurs. The electrical characteristics of my new rectifier are substantially those of an electric arc.

My invention is embodied in a device containing a cathode, of highly refractory material, such, for example, as tungsten, and an anode or anodes having a heat dissipat ing capacity enabling continuous operation at a given rated capacity at a temperature below about 727 (3., at which temperature electron emission is relatively negligible, this device being filled with argon of relatlvely appreciable pressure, preferably of the order of magnitude of atmospheric pressure. excluded.

In the parent application, above identified, I have enumerated various inert gases which may be introduced into a rectifier. Amo marke advantages. or example, an ar in argon exhibits a verylow voltage drop. Under favorable conditions the difference in potential across the electrodes between which the arc is operating is only about one to two volts. Argon being gaseous at ordivoltage range comparable to the range.

much lower pressures a.

. Water vapor should be carefully these gases ar on possesses several nary temperatures protects the incandescent cathode from disintegration at the very start-of the operation of the rectifier, whereas mercury vapor which exhibits the next most favorable Volta e consumption to argon, is condensed to 51c liquid state when the arc is not operating so that some disintegration of the electrodes takes place before the mercury has become vaporized. A bulb filled with argon is also more transportable than one containing mercury.

My invention will be more completely understood by reference to the following description taken in connection with the accompanying drawing of which Figure 1 illustrates a full wave rectifier containing argon; Fig. 2 illustrates one particular form of half wave rectifier, and Fig. 3 is a diagram of suitable electrical connections.

The full wave rectifier shown in Fig. 1 comprises an envelo 1, which conveniently consists of glass and has three side arms 2, 3 and 4, provided for the convenience of scaling in the leading-in conductors. The

cathode conductors 5, 6 may, for example,

consist of tungsten sealed directly into a stem 7 of low-expansion glass, such, for example, as sodium-magnesium bore-silicate, although any convenient seal may be used. The cathode comprises a filament 8 of tungsten, or other highly refractory material, operable at a temperature of at least about 2000 C. The cathode is heated to incandescence during operation from any convenient source of current, for example, a battery as indicated at 16, Fig. '3. In some cases, the heating current may be cut oil after the discharge or are is started, particularly when the gaseous atmosphere is at high pressure, and enough energy will be liberated by the arc to maintain a portion of the'cathode at a sufliciently high incandesc'ence.

A clean, refractory metal, such as tungin a half wave rectifier as shown at 11, Fig. 2. The anodes referably consist of tungsten although ot er highly refractory'materials may be used. The anode terminals 12 also preferably consist of tungsten and may be sealed directly into stems 13, 14; of low expansion glass.

The envelop 1s first very carefully evacuated and baked out at as high a temperature as the glass will stand without softening so as to remove residues of air and water vapor. Unless the anodes have been freed from gas previous to mounting, for example, by heat ing to a high incandescence in a vacuum, they should be freed from deleterious gases in the tube by'electron bombardment by impressing between the cathode while at incandescence and the anode to be purified a voltage high enough to cause an electron current to flow but insuflicient to produce appreciable positive ionization. Deleterious gases are thereby driven out of the anode. The evacuation may then be continued and the voltage progressively increased as gas is removed. ThlS method is disclosed and claimed in an application, Serial No. 795,610 filed by Irving Langmuir.

' A uantity of argon is then introduced into t e envelop. The gas is preferably at a relatively considerable pressure, for example, at a pressure varying from about one centimeter of mercury pressure upward to atmospheric pressure. N0 definite lower limit of pressure can be assigned, but the pressure should be high enough to largely suppress electrical disintegration of the cathode by the bombardment of ions.

When the gaseous pressure is low it is practically necessary to provide for greater electron emission at the cathode than neces sary to convey the current, for example, by increasing the temperature of the cathode. Thereby a negative field is established about the cathode, and the bombardment of the cathode by positive ions, and its disintegration is reduced by the presence of these elec trons which apparently return to the cathode.

At the higher pressures the electrical disintegration, or sputtering, of the cathode is correspondingly less and the useful life of the device is correspondingly longer, so that a high electron emission is not necessary to give a long life although, of course, a high electron emission may also be employed even at higher gas pressures. The thermal disintegration is also less at higher gas pressures. As the pressure of the gas increases beyond a certain limit varying with the nature of the gas, and which as in the case of argon is somewhat less than one centimeter of mercury pressure, the voltage drop in the tube increases. In most cases, however, it is desirable to operate at a gas pressure substantially above the region of minimum. voltage drop in order to secure a fair life.

However, when currents of low voltage are to be rectified and the highest efliciency is desired, the voltage dro permissible may make it desirable to secrihce life to efliciency to some extent, and therefore, to operate at the pressure of minimum voltage drop, but ordinarily this is not desirable.

As shown in Fig. 3, the anodes 9, 10 may be connected to the terminals of a source of alternating current, such as the secondary of a transformer 17, the cathode 8 being connected to an intermediate point of potential in series with a load 18, and a series resistance 19. The device is started after suitable connections have been made by closing the switch 20 in the heating circuit 21 and heating the cathode to incandcscence.

he anodes should be made of such size that heat will be dissipated from them at such rate that they will remain below the temperature at which appreciable electron emission occurs so as to prevent passage of current in the reverse direction when the anode is negative.

With the rectifier constructed as illustrated and above described, currents of many amperes dependi on the size of the apparatus can be rectifie without discharge of any current in the reverse direction with a low voltage drop, which in argon is about 1 to 2 volts, and which varies somewhat dependent upon the temperature of the cathode, pressure of the gas, and similar conditions. When the current to be rectified has a voltage up to several hundred volts, the cathode and anodes are located relatively close together, as indicated in the drawing, but when the voltage is substantially hi her than this the distance between the ca ode and the anodes should be correspondingly increased.

The thermionic discharge is normally confined to a relatively narrow zone between the cathode and the anode, and has the general appearance of an ordinary open air arc. The electrical operating characteristics of the device are those of an arc, that is, an increase of current produces little appreciable instantaneous change of voltage. However, inasmuch as an increase also increase the gas pressure, an increase of current is accompanied by an increase of voltage drop if suflicient time has elapsed for an adjustment of pressure. The instanof current will I taneous value of the Voltage across the ter- 1 minals must be lowered by an increase of current, as two rectifiers cannot be operated in parallel without some provision being made to divide the load.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. A rectifier comprising the combination of a sealed envelop, a refractory cathode operable at a temperature of at least about 2000 (1., an anode having a heat-dissipatcapacity great enough to be operable be ow the temperature at which ap reciable electron emission occurs, and a of argon having at the operating temperature of the device a presure materially above one millimeter of mercury.

2. A rectifier comprising the combination of a sealed envelop, a tungsten cathode, means for heating said cathode to incandescence, an anode having a heat-dissipating capacity'great enough to be operable below the temperature at which ap reciable electron-emission occurs, and; a of argon having at the operating tem erature of the device a pressure of at least a ut one centimeter of mercury.v

3. A rectifier comprising. the combination of a sealed envelop, a refractory cathode adapted to emit electrons, an anode having a heat-dissipating capacity great enough to havlng a be operable below the temperature atiivhioh appreciable electron emission occ1n's,;and a uantity of argon in said envelgg havingat t e operating temperature of device a pressure suificiently high to give to an elec-.

trical discharge emanating from the cathode when at incandescence the char t i the cathode at incan escence. 1 "In witness whereof, I have hereunto set my hand this 14th day of Janna GEORGE STANLEY 1916. IKLE. 

